1. Field of the Invention
The present invention relates to a control device for a hydraulic drive winch for controlling rotation of a winch drum driven by a hydraulic motor.
2. Description of the Related Art
A conventional control device for a hydraulic drive winch is shown in Japanese Patent Application Laid-Open No. 63-35555 Publication. That is, in the aforesaid device, a winch drum is provided with a clutch, and both negative and positive brakes. These clutch and brakes are on/off controlled according to the operating conditions of drum drive and stop, and free fall (free fall of suspended load). For the free fall, the clutch, the positive brake and a control system for them are necessary. This poses a problem that the device constitution becomes complicated, and the cost is high.
So, we have proposed a device for eliminating the clutch and brakes for the free fall. This device is shown in Japanese Patent Application Laid-Open No. Hei 11-79679 Publication. By setting a motor to a small capacity during the free fall operation, the winch drum can be wound down and rotated at high speeds.
Incidentally, a hydraulic pump, which is a hydraulic source for a hydraulic motor, is not exclusively used for a winch but is used in common as a hydraulic source for a plurality of actuators. Therefore, the engine speed is changed by the total of loads of the actuators. The pump flow rate is changed by the change of the engine speed. The motor flow rate is changed accordingly. The motor flow rate is changed at a position of the same control valve during the free fall operation. Therefore, when the engine speed is risen, the motor speed exceeds the allowable speed so that there sometimes possibly occurs the situations such that the winding-down speed is excessively high, and the random winding occurs.
As the winding-down operating means for operating the control valve on the winding-down side, the present inventors have provided, separately from the first winding-down operating means for normal winding-down, the second winding-down operating means for free fall operation. The second winding-down operating means controls the passage flow rate of the control valve so that the flow rate of the hydraulic motor does not exceed the allowable flow rate at the minimum valve of the motor capacity. The passage flow rate of the valve (motor flow rate) is controlled by operating the control valve by the second winding-down operating means during the free fall operation.
Accordingly, the excessive rotation can be prevented while keeping the motor flow rate properly.
In this case, as the winding-down operating means, there are two operating means, i.e., normal winding-down and free fall operation. Therefore, in the operation for continuously carrying out the winding-up operation and the free fall operation, the operation becomes complicated.
Further, where the winch drum is wound down and rotated at high speeds by setting the motor to a small capacity during the free fall operation, the speed when winding-down starts becomes quick as the load of a hanging load increases. Where a rapid lever operation is carried out, a shock possibly occurs in the vehicle body. Furthermore, when the initial speed is high, the movement of a counter balance valve cannot follow the hanging load, and hunting possibly occurs.
It is a first object of the present invention to provide a control device for a hydraulic drive winch capable of preventing excessive speed of a motor caused by an increase in engine speed during the free fall operation and capable of using winding-down operating means for normal winding-down operation and free fall operation is common.
It is a second object of the present invention to provide a control device for a hydraulic drive winch occurring no shock at the time of starting winding-down because initial speed is low even where a load of a hanging load is heavy and also capable of preventing occurrence of hunting.
The control device for a hydraulic drive winch according to the present invention has the following fundamental constitution. That is, the control device comprises a winch drum, a variable capacity type hydraulic motor for driving the winch drum, a hydraulic pump as a hydraulic source, a control valve for controlling supply and discharge of pressure oil to the hydraulic motor, winding-up side for operating the control valve on the winding-up operating means, motor capacity control means for controlling capacity of the hydraulic motor, and free fall instructing means for outputting free fall instructions. The motor capacity control means is operated on the basis of the free fall instructions from the free fall instructing means to set the hydraulic motor to a small capacity, in which state the winding-down operating means is operated whereby the winch drum is wound down and rotated at high speeds to carry out the free fall operation.
In this case, looseness of a rope and random winding can be prevented.
Preferably, control valve controlling means is provided in addition to the above-described fundamental constitution. The control valve controlling means controls an opening degree of the control valve relative to the operating amount of the winding-down operating means to be smaller than that of the normal winding-down operation without the free fall instructions so that at the time of the free fall operation, the supply flow rate to the hydraulic motor is less than the allowable flow rate of the hydraulic motor.
In this case, at the time of the free fall operation, an opening degree (passage flow rate) of the control valve with respect to the operating amount of the winding-down operating means is throttled. Thereby, the excessive speed of the motor at the time of the free fall operation can be prevented. Accordingly, it is possible to prevent the random winding from occurrence.
In the control device for a hydraulic drive winch according to the present invention, alternatively, the motor capacity control means in the above-described fundamental constitution may employ the following constitution. In this motor capacity control means, the motor capacity is increased on the high engine speed side according to the engine speed for driving the hydraulic pump, whereby at the time of the free fall operation, the hydraulic motor speed is controlled to no more than the allowable speed of the hydraulic motor.
In this case, the motor capacity increase as the engine speed rises. Accordingly, it is possible to prevent the excessive speed of the motor at the time of the free fall operation.
The control device for a hydraulic drive winch may comprise, in addition to the above-described fundamental constitution, free fall control means. The free fall control means changes the capacity of the hydraulic motor from a large capacity to a small capacity in proportional to the operating amount of the winding-down operating means.
In this case, when the free fall operation is selected by the free fall instructing means, a tilting angle of the variable capacity motor is controlled, for example. Thereby, the capacity of the variable capacity motor is set from a large capacity to a small capacity in proportional to the winding-down operating amount. So, when the winding-down operation is carried out using the operating means which is common in operation to the free fall operation, the initial speed of the free fall gets slow since at the time of starting free fall operation, the capacity of the variable capacity motor is large. Accordingly, the free fall operation can be carried out safely.